From: imbibe@mindspring.com   
      
   Otto Robert Frisch (1904–1979) was an Austrian-born British physicist who   
   worked on nuclear physics. With Otto Stern and Immanuel Estermann he first   
   measured the magnetic moment of the proton. With Lise Meitner he advanced the   
   first theoretical    
   explanation of nuclear fission (coining the term) and first experimentally   
   detected the fission by-products. Later, with his collaborator Rudolf Peierls   
   he designed the first theoretical mechanism for the detonation of an atomic   
   bomb in 1940.   
      
   In 1944 at Los Alamos, one of Frisch's tasks as the leader of the Critical   
   Assemblies group was to accurately determine the exact amount of enriched   
   uranium which would be required to create the critical mass, the mass of   
   uranium which would sustain a    
   nuclear chain reaction. He did this by stacking several dozen 3 cm bars of   
   enriched uranium hydride at a time and measuring rising neutron activity as   
   the critical mass was approached. The hydrogen in the metal bars increased the   
   time that the reaction    
   required to accelerate. One day Frisch almost caused a runaway reaction by   
   leaning over the stack, which he termed the "Lady Godiva assembly". His body   
   reflected neutrons back into the stack. Out of the corner of his eye he saw   
   that the red lamps that    
   flickered intermittently when neutrons were being emitted, were 'glowing   
   continuously'. Realizing what was happening, Frisch quickly scattered the bars   
   with his hand. Later he calculated that the radiation dose was "quite   
   harmless" but that if he "had    
   hesitated for another two seconds before removing the material ... the dose   
   would have been fatal". "In two seconds he received, by the generous standards   
   of the time, a full day's permissible dose of neutron radiation." In this way   
   his experiments    
   determined the exact masses of uranium required to fire the Little Boy bomb   
   over Hiroshima.   
      
   He also designed the "dragon's tail" or "guillotine" experiment in which a   
   uranium slug was dropped through a hole in larger fixed mass of uranium,   
   reaching just above critical mass (0.1%) for a fraction of a second. At the   
   meeting to approve the    
   experiment, Richard Feynman, commenting on the transient danger involved, said   
   it was "just like tickling the tail of a sleeping dragon." In the period of   
   about 3 milliseconds, the temperature rose at a rate of 2000 °C per sec and   
   over 10 to the 15th    
   power excess neutrons were emitted.   
      
   https://en.wikipedia.org/wiki/Otto_Robert_Frisch   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)